Storage of normally gaseous material in subterranean caverns



Sept. 2, 1969 G. M. cLoss ET AL 3,464,219 STORAGE OF NORMALLY GASEOUSMATERIAL IN SUBTERRANEAN CAVERNS Filed April 17, 1968 INVENTORS'.

Lilli SY Y S W OR A LE CH O @D ,/U o A EK m United States Patent US. Cl.62-45 7 Claims ABSTRACT OF THE DISCLOSURE A normally gaseous materialhaving a low critical temperature is stored in liquid phase in asubterranean cavern,

by placing the material in a pressure-resistant receptacle.

located in the cavern, and surrounding this receptacle with a differentmaterial having a much higher critical temperature, this latter materialbeing chilled to a temperature substantially below the criticaltemperature of the first material. The latter material may be a normallygaseous material which is stored in liquid phase in the cavern.

This invention relates to the storage of normally gaseous material insubterranean caverns, and more particularly concerns the use ofsubterranean caverns for storing in liquid phase normally gaseousmaterial which has a critical temperature below the normal walltemperature of the subterranean cavern. The invention has particularutility for the storage of ethylene in liquid form.

Subterranean caverns which have been prepared by mining out rock from asolid rock formation, or by washing out salt from a salt deposit, havebeen used for the storage of hydrocarbons. Such caverns generally aresituated at depths ranging from 300 to 3,000 feet below ground level,and the normal temperature of the cavern walls typically is in the rangeof 60-85 F., depending upon the depth of the cavern. When thehydrocarbon ma terial has a critical temperature above the normal cavernwall temperature, it is stored in the cavern as a liquid. Thus, normallygaseous hydrocarbons such as propane and butane conventionally arestored in subterranean caverns under sufficient pressure to maintain thehydrocarbon in liquid phase, since their critical temperatures (about204 F. and about 307 B, respectively) are well above the normal cavernwall temperature. However, ethylene (which has a critical temperature of49.5" F., below the normal cavern wall temperature) presents a problem.It is desirable to be able to store this material as a liquid ratherthan as a gas, since in the case of a gas the amount of material thatcan be stored in a cavern of given size is considerbly less than in thecase of a liquid. The problem is then to continuously maintain theethylene at a temperature below its critical temparature, in spite ofthe normally higher Wall temparature of the cavern.

The storage of ethylene in subterranean caverns presents anotherproblem, which is due to its high vapor pressure. At 32 F., the vaporpressure of ethylene is 40.6 atmospheres, it being remembered that oneatmosphere is equivalent to 760 mm. of mercury pressure; at 4 F., thevapor pressure is 24.8 atmospheres; even at the low temperature of 40F., the vapor pressure of this material is quite high, being 14.2atmospheres. This means that for conventional storage of the ethylene asa liquid under pressure in a subterranean cavern, an excessive pressurewould have to be used in the cavern, or else the ethylene would have tobe refrigerated to an inordinately low temperature. For various reasons,it is desirable to avoid exerting a dangerously high pressure 3,464,219Patented Sept. 2, 1969 on the shaft leading to the cavern, and therefrigeration of the ethylene to such low temperatures as would benecessary to avoid the use of such high pressures would be impracticaland uneconomic.

The present invention provides a novel method of and arrangement forstoring a light hydrocarbon such as ethylene as a liquid in subterraneancaverns havin a normal wall temperature which is above the criticaltemperature of the hydrocarbon. The arrangement is such that bothexcessive pressures and any necessity for refrigerating to aninordinately low temperature, are avoided. In the arrangement of theinvention, ethylene and a higher critical temperature (and higherboiling) hydrocarbon are simultaneously stored in a subterranean cavern,both in the liquid phase. While the invention is particularly applicableto the storage of ethylene, it can also be used for storing othernormally gaseous materials that have a critical temperature below thenormal wall temperature of the cavern, for example, silicon tetrahydrideof xenon. In this connection, it is noted that the vapor pressure ofxenon is comparable to that of ethylene. The invention can also be usedfor the liquid phase storage of ethane, in a situation where the normalcavern wall temperature is above the critical temperature F.) of thishydrocarbon.

According to this invention, a pressure-resistant storage receptacle ispositioned in the cavern, and the ethylene is placed as a liquid in thisreceptacle, for storage. A different material, whose criticaltemperature is above the normal temperature of the cavern walls, isstored as a liquid in the cavern, around the ethylene storagereceptacle. The last-mentioned material, which is in thermal contactwith the ethylene receptacle, is chilled to a temperature substantiallybelow the critical temperature of the ethylene. The last-mentionedmaterial is prefera-bly a normally gaseous hydrocarbon.

A detailed description of the invention follows, taken in conjunctionwith the accompanying drawings, wherein:

FIG. 1 is a schematic illustration of an arrangement according to thepresent invention; and

FIG. 2 is a simplified schematic illustration of a modified arrangement.

Referring first to FIG. 1, numeral 1 indicates a subterranean cavernwhich has been prepared either by mining out a rock formation, or bywashing salt from a rock salt deposit; for convenience, the cavern isillustrated as being in a rock formation such as granite. Positioned incavern 1 are one or more (three are illustrated in FIG. 1) storagereceptacles 2 that are pressure-resistant, or in other words than canwithstand a relatively high pressure. The receptacles can take the formof a plurality of relatively small storage tanks (as illustrated in FIG.1), or a coil of large-diameter pipe, or a series of pipes, any of whichwould provide sufficient volume for the desired ethylene storagecapacity. Preferably, the receptacles 2 are made of a highheat-conductivity material, such as a suitable metal.

The inlet connections of the receptacles 2 may be manifolded undergroundas illustrated, and an inlet line 3 having a pump 4 therein leads fromthe surface to the manifolded receptacle inlets. Through pump 4, line 3i connected to an ethylene storage tank (not shown) through a chiller(not shown) adapted to reduce the temperature of the ethylene to thedesired low level, such as 15 F. Line 3 and pump 4 enable liquefiedethylene to be fed into the receptacles 2, for storage as a liquidtherein.

The outlet connections of the receptacles 2 (indicated as being at thelower ends of the tanks) are manifolded underground, and an outlet line5 connected to a subterranean (and submersible) pump 6 is provided forwithdrawal of the stored ethylene from the ethylene storage receptacles.

Since the storage receptacles 2 (which are designed to withstand arelatively high pressure) are sealed off from the walls of cavern 1 andare thus isolated therefrom, it may be seen that excessive pressures onthe cavern walls, or on the shaft (not shown) leading there to, areavoided.

According to one aspect of this invention, a normally gaseous material,whose critical temperature is above the normal temperature of the cavernwalls, is stored as a liquid body 7 in the cavern interior space, thisliquid body surrounding the storage receptacles 2 and being in thermalcontact therewith. An inlet line 8 having a valve 9 and connected to apump 10 is provided for introducing the liquid 7 into the cavern, line 8being connected by way of a valve 11 to a suitable storage tank whenthis liquid is being introduced into cavern 1. An outlet line 12 havinga valve 13 and connected to a subterranean (and submersible) pump 14 isprovided for withdrawing the liquid 7 from the cavern, line 12 beingconnected by way of a valve 15 to a surface outlet line 16 when thisliquid is being withdrawn from cavern 1.

The material utilized for the liquid body 7 is preferably selected fromthe C -C hydrocarbon group, comprising propylene, propane, isobutane,n-butane, l-butene, 2-butene, and Z-methyl-propene, the last three ofwhich are known collectively as butenes or the butylenes. All of thesehydrocarbons have critical temperatures well above the normal walltemperature of the cavern 1, and so do not present any problem (in thisregard) for their storage in liquid phase in a subterranean cavern. Thecritical temperatures of certain members of the above group are asfollows, all given in degrees Fahrenheit: propylene, 198.1; propane,204.1; isobutane, 273.2; nbutane, 307.4.

The boiling points of the C -C hydrocarbons mentioned are allconsiderably higher than that of ethylene (C H and as a result the vaporpressures of these C -C hydrocarbons are all small compared to that ofethylene, for equivalent temperatures. Therefore, the storage of these C-C hydrocarbons in liquid form in the cavern (even though they arenormally gaseous) does not result in excessive pressures on the walls ofthe cavern, or on the shaft leading thereto. The boiling points of theseC C hydrocarbons are as follows, again in degrees Fahrenheit, ethylenealso being included for purposes of comparison: ethylene, l55;propylene, -52.6; propane, 48.1; isobutane, 14.4; n-butane, 31.5;l-butene, 23; 2-butene, 33.8; Z-methyl-propene, 21.2. For r comparisonwith the vapor pressures given hereinabove for ethylene, the followingvapor pressures are given for some C -C hydrocarbons: propylene atapproximately -30 F., 1307 mm. of mercury; isobutane at -4 F., 646 mm.of mercury.

Preferably, the C -C hydrocarbon liquid 7 is kept refrigerated to atemperature substantially below 495 R, which temperature, as previouslystated, is the critical temperature of ethylene. This may be done bymeans of a chiller 17, whose inlet is coupled through valve 18 to line12 and whose outlet is connected through valve 19 to line 8. Thus, theliquid 7 may be pumped from the cavern 1 to chiller 17 by means of pump14, by way of valves 13 and 18; the chilled liquid may be returned tothe cavern by pump 10, through valves 19 and 9.

Subterranean caverns usually contain free water. As a result, the C Chydrocarbon liquid 7, initially at least, contains water, which couldinterfere with the refrigeration of the liquid 7 (by the formation ofice, for example). This problem may be eliminated by passing therefrigerant liquid 7 through a liquid-phase-dryer 25 (which removes thewater from the hydrocarbon liquid), before the refrigerant enters thechiller 17.

As a result of the chilling or cooling (of the hydrocarbon liquid 7)previously described, this chilled high boiling hydrocarbon 7, which isin thermal relationship with the stored ethylene via the walls ofreceptacle 2, serves to refrigerate the ethylene and hold the latterbelow its critical temperature, so that it can be maintained in liquidphase. The ethylene must be kept below 495 F. by means of thisrefrigeration, but this is obviously not an inordinately lowtemperature.

Instead of the chiller 17, a conventional auto-refrigeration arrangementmay be used for refrigerating the hydrocarbon liquid 7, a dryerpreferably being used in this case, also, prior to the refrigerationunit.

In some instances, it might not be necessary to refrigerate the liquid 7in order to maintain the ethylene below its critical temperature. Insuch instances, the chiller 17 could be dispensed with, and thereceptacles 2 would be provided with vacuum jackets to reduce heattransfer to the stored ethylene; the ethylene would be chilled to afairly low temperature before being placed for storage in receptacles 2.

Refer now to FIG. 2, which illustrates a modified arrangement accordingto the invention. In the figure, elements the same as those of FIG. 1are denoted by the same reference numerals, while elements similar tothose of FIG. 1 are denoted by the same reference numerals butbearing aprime designation. Positioned in subterranean cavern 1' are two storagereceptacles 2 and 20 that are pressure-resistant, and which may be smallstorage tanks as illustrated, or may be pipes, as previously mentionedin connection with FIG. 1. Line 3 and pump 4, coupled to receptacle 2,enable liquefied ethylene to be fed into this receptacle, for storage asa liquid therein. Line 5 and pump 6, coupled to receptacle 2, enablewithdrawal of the stored ethylene from this receptacle.

An inlet line 21 having a pump 22 therein leads from the surface to theinlet connection of receptacle 20. Through pump 22, line 21 is connectedto a storage tank (not shown containing a C -C hydrocarbon (for example,propylene, butylene). Line 21 and pump 22 enable the liquefied C -Chydrocarbon to be fed into receptacle 20, for storage as a liquidtherein.

The outlet connection of the receptacle 20 (indicated as being at thelower end of this tank) is connected through a subterranean pump 23 toan outlet line 24; this arrangement provides for withdrawal of thestored C -C hydrocarbon from receptacle 20.

Another C -C hydrocarbon (for example, butane) is stored as a liquidbody 7 in the cavern interior space, surrounding the storage receptacles2 and 20. Inlet line 8, valve 9, and pump 10 (not shown) enable theliquid 7 to be fed into the cavern interior, while outlet line 12andpump 14 enable the stored liquid 7 to be withdrawn from the cavern.

In the FIG. 2 embodiment, the liquid 7 could be chilled as described inconnection with FIG. I, and used to refrigerate the ethylene stored inreceptacle 2, thereby holding the latter below its critical temperatureso that it can be maintained in liquid phase.

Summarizing, the embodiment of FIG. 2 represents an arrangement forstoring three different hydrocarbons (one of which is ethylene) inliquid phase in a subterranean cavern.

The invention claimed is:

1. In the storage of a first normally gaseous material in a subterraneancavern the walls of which normally have a temperature above the criticaltemperature of said material, the method of storing said material inliquid phase which comprises placing said material as a liquid in thecavern interior space while isolating such liquid from the cavern walls,storing as a liquid in the cavern interior space, and in thermalrelationship with said material, a second material whose criticaltemperature is above the normal temperature of the cavern walls, andrefrigerating said second material to a temperature substantially belowthe critical temperature of said first material.

2. Method according to claim 1, wherein said first material is ethylene.

3. Method according to claim 1, wherein said second material is C -Chydrocarbon.

4. Arrangement for storing a first normally gaseous material in asubterranean cavern the walls of which normally have a temperature abovethe critical temperature of said material, comprising apressure-resistant receptacle positioned in said cavern, means forfeeding said material as a liquid into said receptacle, means forremoving the material from said receptacle, and means for feeding as aliquid into the cavern interior space surrounding said receptacle, andin thermal contact therewith, a second material whose criticaltemperature is above the normal temperature of the cavern walls, saidsecond material being chilled to a temperature substantially below thecritical temperature of said first material.

5. Arrangement according to claim 4, wherei said first material isethylene.

References Cited UNITED STATES PATENTS 2,440,930 5/1948 Camilli et al.6250'2 2,947,147 8/1960 Johnson 6l0.5 3,350,888 11/1967 Shrier 610.53,163,013 12/1964 Webster 6245 FOREIGN PATENTS 914,193 12/ 1962 GreatBritain.

LLOYD L. KING, Primary Examiner

